Why can't I cancel an order that is part/fully received or part/fully invoiced?

My business has used the POP module in Sage 200 for a number of years and I only recently explored he possibility of using it for commitment reporting, i.e. goods received not invoiced, value of outstanding orders etc. However as we have not used the module in this fashion before I have found it in a complete mess. I have live orders that are going back years that are never going to be fulfilled many are partially receipted/invoiced and are just sitting in POP and will never be progressed.

I have read within the Sage help files that you cannot cancel an order that is part/fully received or part/fully invoiced? Does anyone know why this is the case as it seems illogical and has anyone found a simple work around? Posting dummy invoices and credits to complete the orders is not practical given the volume.